Conical air filter

ABSTRACT

An air duct system includes a conical fabric filter disposed within a cylindrical air duct. In some embodiments, both the filter and the air duct are inflatable. A fabric collar and a pair of zippers not only allow the filter to be readily removed for cleaning, but also allow the air duct system to continue operating with the filter removed. Pleats can provide the filter with more surface area, and the pleats can be interconnected in an alternating pattern to inhibit the filter from over inflating.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The subject invention generally pertains to air filters and morespecifically to a fabric filter for use inside an air duct.

[0003] 2. Description of Related Art

[0004] Fans or blowers are used along with ductwork to circulate airthrough a room or area of a building. The blower typically draws airfrom within the room through a return air duct and then forces the airback into the room through a supply air duct. To heat or cool the air,the blower may also force or draw the air across a heat exchanger.

[0005] To help prevent dust from accumulating on the heat exchanger,blower, and ductwork, often a conventional filter is installed at thedownstream end of the return air duct. Finer, less porous filters areused where dust removal is more critical, such as in so called cleanrooms or in buildings having occupants with dust-related allergies.Unfortunately, fine filters usually create a higher pressure drop thatreduces the amount of airflow. To minimize the pressure drop, a filter'seffective cross-sectional area can be increased in various ways, such asby adding pleats to the filter, installing the filter at an anglerelative to the duct, or by forming the filter as an elongated bag thatextends lengthwise into an air duct.

[0006] Some examples of filters that are elongated along the directionof airflow are disclosed in U.S. Pat. Nos. 2,853,154; 3,151,962;3,195,296; 3,204,391; 3,204,392; 3,396,517; and 3,538,686. When mountingsuch filters within a return air duct, upstream of the blower, asignificant distance is needed between the blower and where the filterattaches to the duct, simply due to the length of the filter. In manycases, this can be difficult or impossible to do, because of bends orelbows in the ductwork. Also, much of the ductwork is usuallyinaccessible, as it is often installed within the walls of the buildingor between the floor and ceiling. So filters in a return air duct aretypically installed immediately adjacent the blower, which may prohibitthe use of an elongated filter or at least significantly limit itslength.

[0007] On the other hand, if an elongated air filter were installed inthe supply air duct, the filter would do little in preventing dust fromaccumulating on the blower and the heat exchanger, because dust oftenoriginates in the room. With a filter installed in the supply air duct,dust from the room could pass across the blower and heat exchangerbefore ever reaching the filter.

[0008] Moreover, if elongated filters of current designs were installedwithin a generally cylindrical duct having a pliable fabric wall, thenon-conical shape of the filter may cause the fabric of the duct toflutter, due to uneven patterns of airflow velocity. If thecross-sectional area of airflow between the exterior of an elongatedfilter and the interior of the cylindrical fabric duct is notcircumferentially uniform, as could be the case with a flat-sided filterwithin a cylindrical duct, localized areas of higher velocity may exist.Also, abrupt changes in velocity along the length of a fabric duct mayalso cause the fabric to flutter.

SUMMARY OF THE INVENTION

[0009] In some embodiments, an air duct system includes a conical filterdisposed within a cylindrical duct.

[0010] In some embodiments, an air duct system includes an inflatableconical filter with pleats.

[0011] In some embodiments, the pleats are interconnected in analternating pattern of connection points to inhibit the filter frombillowing excessively outward.

[0012] In some embodiments, an air duct system includes a blower and aheat exchanger interposed between an upstream pre-filter and adownstream conical filter, which is less porous.

[0013] In some embodiments, an inflatable fabric filter is disposedwithin an inflatable fabric air duct.

[0014] In some embodiments, the fabric wall of the air duct is airpermeable.

[0015] In some embodiments, the integrity of a fabric air duct can bemaintained regardless of whether the elongated filter is attached to theduct.

[0016] In some embodiments, a zipper removably attaches an elongatedfilter to a fabric air duct.

[0017] In some embodiments, a plurality of conical filters have the samelength to diameter ratio even though the filters are of differentdiameters for various diameter air ducts.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a cutaway view of an air duct system with a fabric airduct and a conical fabric filter.

[0019]FIG. 2 is a cutaway view of an air duct system with a relativelyrigid air duct and a conical fabric filter.

[0020]FIG. 3 is similar to FIG. 1, but with the fabric duct and filterdeflated.

[0021]FIG. 4 is a perspective view of the filter used in the air ductsystem of FIG. 1.

[0022]FIG. 5 is a closer up view of the supply air duct and conicalfilter of FIG. 1.

[0023]FIG. 6 is similar to FIG. 5, but with the filter removed and twosections of the supply air duct zipped together.

[0024]FIG. 7 is similar to FIG. 4, but showing a fabric conical filterthat is pleated.

[0025]FIG. 8 is a cross-sectional view taken along line 8-8 of FIG. 7.

[0026]FIG. 9 shows one of a plurality of conical air filters.

[0027]FIG. 10 is similar to FIG. 9, but showing a larger filter with thesame length to diameter ratio.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] An air handling system 10 of FIGS. 1 is used to heat or cool anarea 12 of a building 14. To do this, system 10 includes a blower 16; aheat exchanger 18; a pre-filter 20; a finer, less porous inflatablefilter 22; a supply air duct 24; and a return air duct 26. Heatexchanger 18 is schematically illustrated to represent any device forheating or cooling air, such as by electrical resistance or by heattransfer with another fluid, such as refrigerant, water, or glycol. Ahousing 28 can enclose one or more of the components of system 10.

[0029] In operation, blower 16 draws air 30 from area 12, through returnair duct 26 and across pre-filter 20, with pre-filter 20 being anyconventional filter known to those skilled in the art. Pre-filter 20 canbe used to capture the larger dust particles in the air that mightotherwise accumulate on heat exchanger 18 and blower 16. Pre-filter 20also helps prevent large dust particles from quickly plugging up theless porous filter 22 in supply air duct 24.

[0030] After the air passes through pre-filter 20, blower 16 draws theair across heat exchanger 18. Blower 16 then discharges the air throughinflatable filter 22, through supply air duct 24, and into area 12through the pores or other openings in supply duct 24. Filter 22, beingrelatively fine, can be used to remove smaller dust particles that wereable to pass through pre-filter 20. In some embodiments, the fabricmaterial of filter 22 is provided by 3M of St. Paul, Minn., and has astandard particle removal efficiency of 80 to 90%, at 150 to 300cfm/ft², with a static pressure drop of 0.2 inches of water.

[0031] Conical fabric filters, such as filter 22, can be installedwithin various types of ducts. The supply air duct can be made of sheetmetal or some other relatively rigid material, as is the case of conicalfilter 22′ in supply air duct 32 of FIG. 2, or can be made of a pliablefabric 34, as is the case of duct 24. With a metal air duct, airregisters 36 provide one or more openings for air to discharge into area12. As an alternative or in addition to registers 36, the fabric of airduct 24 may be air-permeable and/or be provided with cutouts ordischarge openings 38 that deliver air to area 12. Examples of fabricair duct 24 are disclosed in U.S. Pat. Nos. 5,655,963 and 5,769,708,which are specifically incorporated by reference herein.

[0032] In the example of FIG. 1, the fabric wall of duct 24 has agenerally cylindrical or tubular shape when inflated by the dischargepressure of blower 16. However, when the heating or cooling demand ofarea 12 has been satisfied, blower 16 may turn off, which deflatesfilter 22 and leaves the fabric walls of duct 24 hanging relativelylimp, as shown in FIG. 3. Some fabric air ducts have a rigid frame thathelps hold the fabric walls of the duct in a generally tubular shapeeven when the blower is not running. Such frame-supported ducts are alsowell within the scope of the invention.

[0033] Filter 22 can be installed within an air duct (metal or fabric,supply or return) in various ways. In a currently preferred embodiment,a collar 40, made of fabric or some other material, couples filter 22 toa first segment 24 a and a second segment 24 b of fabric air duct 24.Referring further to FIG. 4, fabric rim 42 at a base 44 of filter 22 issewn or otherwise attached to the interior of collar 40. Collar 40includes two half-zippers 46 and 48 that removably interlock with matinghalf-zippers 50 and 52 on supply air duct 24, as shown in FIG. 5.Half-zippers 46 and 50 comprise a first zipper 54, and half-zippers 48and 52 comprise a second zipper 56. Zippers 54 and 56 allow filter 22 tobe temporarily removed from duct 24 for filter cleaning or replacement.If filter 22 is removed for an extended period, half-zippers 50 and 52may be zipped together to re-establish a continuous supply air duct, asshown in FIG. 6.

[0034] To minimize the pressure drop created by filter 22 and to extendthe period between filter cleanings, filter 22 is elongated to provide alarge surface area though which the air may pass. This is accomplishedby having filter 22, when inflated, be of a generally conical shape(i.e., most of its contour or outer envelope fits the shape of a cone).In some embodiments, filter 22 is in the shape of a cone (i.e.,substantially all of its contour or outer envelope fits that of a cone).

[0035] To help prevent the fabric walls of duct 24 b from fluttering,the velocity and flow direction of the air between the exterior offilter 22 and the interior of duct 24 b is kept as smooth as reasonablypossible. This can be achieved by installing a conical filter within acylindrical duct to create an airflow path whose annular cross-sectionalarea increases gradually from an upstream to a downstream end of filter22.

[0036] To provide a conical filter with more surface area, a filter 58can have a pleated fabric wall, as shown in FIGS. 7 and 8. The pleatsrun generally lengthwise with each pleat being connected to its twoadjacent pleats in an alternating pattern of discrete points. Forexample, a central pleat 60 lies between a first pleat 62 and a secondpleat 64. Central pleat 60 has a central peak 60′ that zigzags betweenan adjacent first peak 62′ and a second peak 64′ of pleats 62 and 64,respectively. Central peak 60′ is attached to first peak 62′ at points66, 68 and 70. Central peak 60′ is also attached to second peak 64′ atpoints 72, 74 and 76. The alternating pattern of connection pointsinhibits the blower's discharge air pressure from flattening the pleatsand restrains filter 58 to a generally conical shape.

[0037] To provide a plurality of conical filters that provide the sameflow rate for a given area of filter material regardless of the duct'sdiameter, each filter's length to diameter ratio is the same. Forexample, in FIG. 9, a filter 78 in a first duct 80 has a diameter 82 of24 inches, as measure along a base 84 of conical filter 78, and has alength 94 of 120 inches, as measured from a center 86 of base 84 to anapex 88 of filter 78. Similarly, in FIG. 10, a filter 90 in a largerduct 92 has a diameter 96 of 48 inches and a length 98 of 240 inches,whereby both filters 78 and 90 have a length to diameter ratio of five(120/24=5, and 240/48=5).

[0038] Although the invention is described with reference to a preferredembodiment, it should be appreciated by those skilled in the art thatvarious modifications are well within the scope of the invention.Therefore, the scope of the invention is to be determined by referenceto the claims that follow.

I claim:
 1. An air duct system for conveying and filtering a stream ofair, comprising: an air duct adapted to convey the stream of air; and aninflatable filter having a generally conical shape when inflated andtraversing the air duct such that substantially the entire stream of airthat passes through the air duct also passes through the inflatablefilter.
 2. The air duct system of claim 1, wherein the inflatable filteris in the shape of a cone.
 3. The air duct system of claim 1, furthercomprising a first zipper that couples the inflatable filter to the airduct.
 4. The air duct system of claim 3, further comprising a secondzipper that couples the inflatable filter to the air duct.
 5. The airduct system of claim 1, further comprising a removable collar attachedto the inflatable filter, wherein the air duct includes an upstream ductand a downstream duct with the removable collar interposed therebetween.6. The air duct system of claim 1, wherein the upstream duct is adaptedto be connected to the downstream duct if the inflatable filter weredisconnected from the air duct.
 7. The air duct system of claim 1,wherein the inflatable filter includes a plurality of pleats that areinterconnected to limit the extent to which the inflatable filter maybillow.
 8. The air duct system of claim 7, wherein the plurality ofpleats includes a first pleat having a first peak, a second pleat havinga second peak, and a central pleat having a central peak and beinginterposed between the first pleat and the second pleat, wherein thecentral peak is attached to first peak and the second peak at a firstpoint and a second point respectively, wherein the first point is spacedapart from the second point.
 9. The air duct system of claim 1, furthercomprising a blower and a pre-filter, wherein the blower with respect toa flow direction of the stream of air is downstream of the pre-filterand upstream of the inflatable filter.
 10. The air duct system of claim9, wherein the pre-filter is more porous than the inflatable filter. 11.The air duct system of claim 1, further comprising a heat exchanger anda pre-filter, wherein the heat exchanger with respect to a flowdirection of the stream of air is downstream of the pre-filter andupstream of the inflatable filter.
 12. The air duct system of claim 11,wherein the pre-filter is more porous than the inflatable filter. 13.The air duct system of claim 1, wherein the air duct comprises a pliablefabric.
 14. The air duct system of claim 13, wherein the pliable fabricis porous.
 15. The air duct system of claim 1, wherein the air duct issubstantially cylindrical.
 16. The air duct system of claim 1, whereinthe air duct defines a plurality of discharge openings.
 17. An air ductsystem for conveying and filtering a stream of air, comprising: anupstream duct adapted to convey the stream of air; a pliable downstreamduct adapted to convey the stream of air; a collar interposed betweenthe upstream duct and the downstream duct; and a filter connected to thecollar and being adapted to filter the stream of air, wherein the filteris generally conical.
 18. The air duct of claim 17, wherein the collaris pliable.
 19. The air duct of claim 17, further comprising a firstzipper that couples the collar to at least one of the upstream duct andthe pliable downstream duct.
 20. The air duct of claim 19, furthercomprising a second zipper that couples the collar to the upstream duct,whereby the first zipper couples the collar to the pliable downstreamduct.
 21. The air duct system of claim 17, wherein the upstream duct isadapted to be connected to the pliable downstream duct if the collarwere disconnected from the upstream duct and the pliable downstreamduct.
 22. The air duct system of claim 17, wherein the filter includes aplurality of pleats that are interconnected to limit the extent to whichthe filter may billow.
 23. The air duct system of claim 22, wherein theplurality of pleats includes a first pleat having a first peak, a secondpleat having a second peak, and a central pleat having a central peakand being interposed between the first pleat and the second pleat,wherein the central peak is attached to first peak and the second peakat a first point and a second point respectively, wherein the firstpoint is spaced apart from the second point.
 24. The air duct system ofclaim 17, further comprising a blower and a pre-filter, wherein theblower with respect to a flow direction of the stream of air isdownstream of the pre-filter and upstream of the filter.
 25. The airduct system of claim 24, wherein the pre-filter is more porous than thefilter.
 26. The air duct system of claim 1, further comprising a heatexchange and a pre-filter, wherein the heat exchanger with respect to aflow direction of the stream of air is downstream of the pre-filter andupstream of the filter.
 27. The air duct system of claim 26, wherein thepre-filter is more porous than the filter.
 28. The air duct system ofclaim 17, wherein the pliable downstream duct is of a porous material.29. The air duct system of claim 17, wherein the pliable downstream ductis substantially cylindrical.
 30. The air duct system of claim 17,wherein the pliable downstream duct defines a plurality of dischargeopenings.
 31. An air duct system for conveying and filtering a stream ofair moving from upstream to downstream, comprising: a pre-filter; ablower downstream of the pre-filter; an inflatable filter downstream ofthe blower; and a first air duct downstream of the inflatable filter.32. The air duct system of claim 31, further comprising a first zipperthat couples the inflatable filter to the first air duct.
 33. The airduct system of claim 3, further comprising: a second air duct upstreamof the first air duct and downstream of the blower; and a second zipperthat couples the inflatable filter to the first air duct.
 34. The airduct system of claim 33, further comprising a removable collarinterposed between the first air duct and the second air duct and beingattached to the inflatable filter.
 35. The air duct system of claim 31,wherein the inflatable filter includes a plurality of pleats that areinter connected to limit the extent to which the inflatable filter maybillow.
 36. The air duct system of claim 35, wherein the plurality ofpleats includes a first pleat having a first peak, a second pleat havinga second peak, and a central pleat having a central peak and beinginterposed between the first pleat and the second pleat, wherein thecentral peak is attached to first peak and the second peak at a firstpoint and a second point respectively, wherein the first point is spacedapart from the second point.
 37. The air duct system of claim 31,wherein the pre-filter is more porous than the inflatable filter. 38.The air duct system of claim 31, wherein the pre-filter is more porousthan the inflatable filter.
 39. The air duct system of claim 31, whereinthe first air duct comprises a pliable fabric.
 40. The air duct systemof claim 39, wherein the pliable fabric is porous.
 41. The air ductsystem of claim 31, wherein the first air duct is substantiallycylindrical.
 42. The air duct system of claim 31, wherein the first airduct defines a plurality of discharge openings.
 43. A method ofproducing a plurality of conical filters, comprising: providing eachconical filter of the plurality of filters with a circular base of aunique diameter; providing each conical filter of the plurality offilters with a unique length, wherein the unique length extends from acenter of the circular base to an apex of each respective conicalfilter; and providing each conical filter of the plurality of filterswith a common length to diameter ratio.